This invention is part of a recent development in the manufacture of relatively large gears having diameters of approximately 2 to 6 feet (0.6 to 2 meters). The most common method of manufacturing bevel and hypoid gears utilizes rotating face-mill type cutting tools. However, this face-mill system has not been used in the manufacture of large gears until quite recently. Instead, large gears have been manufactured by using planing tools. While planing is not as fast or efficient as the face-mill method, a major deterrent to the use of the latter method has been the projected costs related to traditional face-mill cutting tools of sufficient size for manufacturing large gears.
When cutting gears by the face-mill method, it has traditionally been considered preferable to use cutters having radii roughly equivalent to the outer cone distances of the gears being cut. For relatively flat bevel gears (with pitch angles 70.degree. or higher), this traditional cutter diameter is about equal to the diameter of the gear. Since the size and cost of a gear cutting machine varies directly with the maximum size of the cutter it is designed to use, this traditional selection of cutter diameter is not economically practical for cutting gears larger than two feet in diameter.
While it has been known that larger gears could be cut with face-mill cutters having diameters as small as 60% of the gear diameter, it is also well known that should such smaller diameter cutters be used, development work (i.e., minor changes in cutting parameters undertaken to optimize the final shape of the teeth being cut) would often require that many very small changes be made in point diameter (i.e., the radial distances of the cutting edges of the blades from the center of the cutter). Such changes would not only be time-consuming, but would require that large numbers of expensive shims be stocked.
As to another cutting tool parameter, different cutter blade angles are required according to (a) the shape of the gear tooth being cut, (b) the pressure angle relationship desired between the work and tool, (c) the length of the tooth bearing ultimately desired, etc. To obtain such variety of blade angles requires that manufacturers stock a variety of blade sets, the various sets having been manufactured with an appropriate spectrum of commonly needed blade angles.
Further, when cutting spiral bevel gears, the direction of rotation of the cutting tool often changes with different jobs depending upon such things as the direction of the spiral angle of the gear teeth being cut, whether or not it is desired to cut by conventional milling or by climb milling, the direction of the cutting roll, etc., as is well known in the art. In prior art cutting tools, a change in the direction of cutter rotation requires that different cutting blades be used and often requires the use of different cutter bodies as well.
Thus, it can be appreciated from the above remarks that to manufacture a variety of gears with face-mill cutters, a manufacture must have cutting tools which can meet a variety of tool parameters, e.g., different cutting blade angles and blade point diameters, in addition to differing directions of cutter rotation. Further, a single blade used in the cutting of large gears can cost considerably more than an entire set of blades used for cutting smaller gears. Therefore, in spite of the relative advantages, in terms of speed and efficiency, of the face-mill cutting method over planing methods, the expected cost of maintaining an appropriate inventory of cutter bodies, blades, shims, etc., has seemed prohibitive and has been an important deterrent to the use of the face-mill system for large gear manufacture.
The invention disclosed herein helps to solve this problem by providing a versatile cutting tool in which a single cutter body can be used in combination with a single set of cutter blades to provide proper tool parameters for covering a wide variety of different cutting situations.